1. Field of the Invention
The invention relates to a method for dissolving hard-to-dissolve thorium and/or plutonium oxides, especially dioxides such as ThO.sub.2, PuO.sub.2 or (U/Pu)O.sub.2 mixed oxides.
2. Description of the Prior Art
Such a method is known from German Offenlegungsschrift No. 26 19 089, according to which plutonium dioxide (PuO.sub.2) is dissolved in a boiling mixture of concentrated nitric acid (HNO.sub.3) and hydrofluoric acid (HF). The dissolution rates increase with increasing concentration of the hydrofluoric acid. The dissolution takes place, for instance, in dissolving tanks of polytetrafluoroethylene.
With increasing hydrofluoric acid content, this mixture of concentrated nitric acid and hydrofluoric acid attacks not only the plutonium dioxide, but also the walls of the dissolving vessel. If dissolving tanks of metal are used, impurities consisting of corrosion products are additionally noted as a disadvantage in the further processing of the plutonium solution. Furthermore, the added fluorides must be separated again in an additional operation before the plutonium solution is processed further, since they not only stress the processing facilities corrosively, but also inhibit secondary chemical processes. In this connection, it is very difficult to separate the fluoride in thorium and plutonium complex compounds.